Data Flow Diagram

BNO085 Sensor (I2C) → Arduino → [SPI] → FPGA → [SPI] → STM32 MCU

The FPGA acts as a bridge, allowing the Arduino (SPI master) and MCU (SPI master) to communicate through the FPGA’s dual slave interfaces.

SPI Communication Protocol

The system uses SPI Mode 0 (CPOL=0, CPHA=0) with MSB-first bit ordering:

Arduino → FPGA SPI Interface: - Clock Speed: 100kHz - Packet Format: 16 bytes - Byte 0: Header (0xAA) - Bytes 1-2: Roll (int16_t, MSB first, scaled by 100) - Bytes 3-4: Pitch (int16_t, MSB first, scaled by 100) - Bytes 5-6: Yaw (int16_t, MSB first, scaled by 100) - Bytes 7-8: Gyro X (int16_t, MSB first, scaled by 2000) - Bytes 9-10: Gyro Y (int16_t, MSB first, scaled by 2000) - Bytes 11-12: Gyro Z (int16_t, MSB first, scaled by 2000) - Byte 13: Flags (bit 0 = Euler valid, bit 1 = Gyro valid) - Bytes 14-15: Reserved (0x00)

FPGA → MCU SPI Interface: - FPGA passes raw 16-byte packet buffer directly to MCU - MCU reads data via SPI master transactions - FPGA acts as transparent bridge, forwarding data without modification

Key Components

FPGA Implementation: - Top-level module: drum_trigger_top.sv - Arduino SPI slave: arduino_spi_slave.sv - MCU SPI slave: spi_slave_mcu.sv - System clock: 3MHz (48MHz HSOSC divided by 16)

MCU Implementation: - STM32L432KC with SPI1 master configuration - Pins: PB3=SCK, PB5=MOSI, PB4=MISO, PA11=NSS - Reads and processes sensor data from FPGA

Arduino Implementation: - BNO085 sensor interface via I2C (400kHz) - SPI master to FPGA (100kHz, Mode 0, CS pin D10) - 100Hz sensor update rate

Key Source Files

FPGA: - drum_trigger_top.sv - Top-level module - arduino_spi_slave.sv - Arduino SPI slave interface - spi_slave_mcu.sv - MCU SPI slave interface

MCU: - main.c - Main application code - STM32L432KC_SPI.c - SPI driver

Arduino: - ARDUINO_SENSOR_BRIDGE.ino - Sensor bridge code

Finished Design Photos

TODO: Add photos of the complete system

Please add photos showing: - Complete assembled system - FPGA board close-up - MCU board close-up - Arduino/ESP32 setup - Wiring and connections

Recommended Specifications: - Format: JPG or PNG - Size: 1500-2000px width minimum - Location: Save to Images/ directory

Example:

![Complete System](Images/system-assembly.jpg){width="100%" alt="Complete assembled system"}

Video Demonstration

TODO: Add video link or embed

Please add your demonstration video. The video should be: - Hosted in the provided Google Drive folder - Named: <LastName1><LastName2><VideoName> - Shows the complete system in operation

Video Content Should Include: - System overview and setup - Sensor data acquisition demonstration - Data flow through the pipeline - Application-specific functionality

Embedding Options: - Google Drive embed (iframe) - Direct link to Google Drive - YouTube/Vimeo embed

Key Design Decisions

1. FPGA as Bridge Architecture - Allows for data processing and formatting in the FPGA - Provides flexibility for future enhancements - Separates concerns: Arduino handles sensor interface, FPGA handles protocol conversion, MCU handles application logic

2. Dual SPI Slave Design - Allows both Arduino and MCU to act as SPI masters - Simplifies protocol design (no arbitration needed) - Enables asynchronous data flow

3. 16-Byte Packet Format - Fixed size simplifies FPGA buffering logic - Header byte (0xAA) enables packet synchronization - Includes all necessary sensor data

Technical Challenges

Clock Domain Crossing (CDC): - Safely transferring data between asynchronous clock domains (Arduino SCK, FPGA system clock, MCU SCK) - Solution: CS-based safe read approach with 3-cycle delay, providing 10:1 timing margin

SPI Timing Synchronization: - Ensuring proper timing between Arduino SPI master and FPGA SPI slave - Solution: CS-based protocol with proper clock edge detection and header validation

Data Format Consistency: - Maintaining consistent data formats across all stages - Solution: Fixed 16-byte packet format with clear byte assignments